1. Field of the Invention
This invention relates to a sheet separating apparatus provided in an image forming apparatus such as a copying machine, a printer or a facsimile apparatus for separating and feeding out recording sheets and originals one by one.
2. Related Background Art
An image forming apparatus has heretofore been equipped with a sheet separating apparatus for separating and supplying recording sheets and originals one by one to an image forming portion and an original reading portion. In this sheet separating apparatus, use is made of various separating systems such as a separating pawl (claw), a separating pad and a reversely rotating roller in conformity with the separating property, cost, etc.
FIG. 5 of the accompanying drawings shows an example of a sheet separating apparatus adopting a separating system using a separating pad according to the prior art. This will hereinafter be schematically described.
The reference numeral 50 designates a sheet feeding roller which is rotated in the direction of arrow E to thereby feed out recording sheets or originals (hereinafter referred to as sheets) P stacked (piled) on a sheet feeding tray 51 and a pressure plate 52. The pressure plate 52 is supported for pivotal movement in the directions of arrow A-B about a shaft 53, and biases the leading end side of the piled sheets P toward the sheet feeding roller 50 by a spring member, not shown and brings the sheets into pressure contact with the sheet feeding roller 50. The pressure plate 52 is provided with a friction pad 52a for preventing the sheets from being fed out as a bundle when the number of the piled sheets has become small.
A separating pad 54 for separating the sheets is provided on the downstream side of the pressure plate 52 with respect to the sheet feeding direction. This separating pad 54 is held on a pad holder 56 supported pivotally in the directions of arrow C-D about a shaft 55, and is brought into pressure contact with the sheet feeding roller 50 by a separating spring 57.
According to this construction, the sheets brought into pressure contact by the pressure plate 52 are fed out toward the separating pad 54 by the sheet feeding roller 50 being rotated in the direction of arrow E. These sheets thus fed out are separated one by one between the sheet feeding roller 50 and the separating pad 54 and fed toward the downstream side. To reliably separate the sheets in this case, the coefficient of friction between the surface of the separating pad 54 and the surface of the sheet feeding roller 50 must be higher than the coefficient of friction between the sheets, and need generally that .mu. is equal to 1 or greater with the kind of the sheets used and environmental conditions such as temperature and humidity taken into account.
The sheet separating apparatus adopting the above-described separating pad system according to the prior art, however, has suffered from the following problem.
As described above, the coefficient of friction between the sheet feeding roller 50 and the separating pad 54 is sufficiently high for the separation of the sheets. Therefore, if the sheet feeding roller 50 is rotated with no sheet inserted in the nip portion (the portion of pressure contact) between the sheet feeding roller 50 and the separating pad 54, i.e., with the sheet feeding roller 50 and the separating pad 54 directly brought into pressure contact with each other as shown in FIG. 5, a minute slip stick phenomenon may occur between the sheet feeding roller 50 and the separating pad 54 and the separating pad may be vibrated to thereby cause unpleasant noise (chattering sound).